Lanekeeping assistance systems are generally developed for the purpose of improving safety and driving comfort. These systems are for example designed to detect and prevent an unintended lane departure of a vehicle. Lanekeeping assistance systems sense a vehicle's position in a road lane and, in response to the detected position of the vehicle, apply a torque to the steering wheel. The torque that is applied to the steering wheel helps the driver keep the vehicle in the road lane and avoids an unintentional drifting out of the road lane. The tasks that must be performed by a lanekeeping assistance system include the task of sensing a road lane position and the task of providing a feedback torque to the driver. The task of sensing the road lane position of the vehicle can be performed in a satisfactory manner by a number of conventional methods. The road lane position is typically sensed by detecting lane markers on the road that bound the lanes. In this case, a video camera captures an image of the lane markers. The image is then processed to extract the lane markers from the image. U.S. Pat. No. 7,295,682 B2 describes an exemplary embodiment of a lane recognition system. Lane departure warning systems that perform a lane sensing function are for example commercially available under the trademark names SAFETRAC, MOBILEYE and AUTOVUE.
Unlike the task of sensing the lane position, which can be performed satisfactorily with conventional methods, the task of applying a torque to the steering system for providing a lanekeeping assistance in such a way that the vehicle motion is smooth and acceptable to the driver and in such a way that the steering system feels comfortable to the driver has so far not yet been solved in a satisfactory manner.
Conventional lanekeeping assistance systems usually do not achieve the objectives of providing a smooth control and a satisfactory interaction with the driver. Formal control techniques may be used to control a vehicle in the absence of a driver, but these solutions by definition try to remove the influences of disturbances. These formal control techniques essentially treat a driver's steering wheel movement as a disturbance that is to be compensated or eliminated. As a result, solutions that try to remove the influence of the driver or try to override a driver input feel disruptive to the driver. Other solutions have looked at the interaction with the driver and have limited the amount of steering torque to be added or have made other allowances to avoid conflicts with the driver. For example, German Patent Application Publication No. DE 103 12 513 A1 discloses a lanekeeping assistance system which provides a steering torque that is added to the torque generated by the driver. The amount of steering torque that is added is limited automatically in case of fast steering movements by the driver. The steering torque can also be limited by the driver by turning a rotary knob. A disadvantage of limiting the added steering torque is that the thus limited steering torque may not adequately control the vehicle.